Anionic dye having high water-fastness

ABSTRACT

A dye which, in the free acid form, has the formula ##STR1## wherein W is COOH 
     X is selected from H, COOH, SO 3  H, halo, hydroxy, nitro, cyano, C 1-6  -alkyl, C 1-6  -alkoxy and C 1-6  -acylamino; 
     Y is H, COOH or SO 3  H; 
     Z is H, COOH or SO 3  H; 
     R &amp; R 1  are each independently H or C 1-6  -alkyl substituted by 0, 1 or 2 --COOR 2  groups; and 
     R 2  is H or C 1-6  -alkyl; 
     provided that there are at least two COOH groups and that the number of COOH groups is equal to or greater than the number of SO 3  H groups. 
     The dye is adapted for the preparation of inks for use in ink jet printing in which it displays high water-fastness on paper.

This specification describes an invention relating to an anionic dye andparticularly a black anionic dye which has differential water-solubilitydependent upon pH.

According to the present invention there is provided a dye which, in thefree acid form, has the formula: ##STR2## wherein W is COOH

X is H, COOH, SO₃ H, halo, hydroxy, nitro, cyano, C₁₋₆ -alkyl, C₁₋₆-alkoxy, or C₁₋₆ -acylamino;

Y is H, COOH or SO₃ H;

Z is H, COOH or SO₃ H;

R & R¹ are each independently H or C₁₋₆ -alkyl substituted by 0, 1 or 2-COOR² groups;

R² is H or C₁₋₆ -alkyl;

provided that there are at least two COOH groups and that the number ofCOOH groups is equal to or greater than the number of SO₃ H groups.

X is preferably selected from SO₃ H, chloro, bromo, hydroxy, nitro,cyano, C₁₋₄ -alkyl especially methyl, C₁₋₄ -alkoxy especially methoxy,C₁₋₄ -alkylcarbonylamino, especially acetamido and, more especially,from H and COOH.

It is preferred that R² is H, methyl or ethyl.

It is especially preferred that X is H or COOH; R¹ is H; and R is H, CH₂COOH or CH₂ CH₂ COOH.

It is preferred that the dye of Formula I contains from 2 to 4 COOHgroups. It is also preferred that at least one, and more especially atleast two, COOH groups are attached directly to aromatic carbon atoms.

Where X is H, the COOH group on Ring A may be in the ortho, meta or paraposition with respect to the azo group but is preferably in the meta orpara position. However, it is preferred that X is COOH and that the twoCOOH groups are in the 3,5-, 3,4- or 2,5- positions on Ring A.

It is preferred that there are not more than two SO₃ H groups, i.e. thatonly one of X, Y and Z is SO₃ H. It is also preferred that there are thesame number of COOH and SO₃ H groups or an excess of 1 or 2 COOH groups.

Examples of diazo components from which Ring A may be derived are

    ______________________________________                                        2-aminobenzoic acid                                                                            3-amino-6-chlorobenzoic acid                                 3-aminobenzoic acid                                                                            2-amino-4-chlorobenzoic acid                                 4-aminobenzoic acid                                                                            2-amino-5-chlorobenzoic acid                                 2-aminophthalic acid                                                                           3-amino-4-chlorobenzoic acid                                 3-aminophthalic acid                                                                           2-chloro-3-aminobenzoic acid                                 4-aminoisophthalic acid                                                                        2-chloro-4-aminobenzoic acid                                 5-aminoisophthalic acid                                                                        2-amino-5-bromobenzoic acid                                  2-aminoisophthalic acid                                                                        3-amino-4-fluorobenzoic acid                                 2-aminoterephthalic acid                                                                       2-amino-5-methylbenzoic acid                                 2-amino-6-methylbenzoic acid                                                                   3-amino-2-methylbenzoic acid                                 3-methyl-4-aminobenzoic acid                                                                   3-hydroxy-4-aminobenzoic acid                                3-amino-4-methylbenzoic acid                                                                   3-amino-5-hydroxybenzoic acid                                3-amino-4-methoxybenzoic acid                                                                  3-amino-4-hydroxybenzoic acid                                3-methoxy-4-aminobenzoic acid                                                                  2-hydroxy-3-aminobenzoic acid                                2-n-butoxy-4-aminobenzoic acid                                                                 2-amino-4-nitrobenzoic acid                                  2-amino-5-sulphobenzoic acid                                                                   3-nitro-4-aminobenzoic acid                                  2-amino-4-sulphobenzoic acid                                                                   3-amino-5-nitrobenzoic acid                                  2-amino-6-hydroxybenzoic acid                                                                  2-nitro-3-aminobenzoic acid                                  2-hydroxy-5-aminobenzoic acid                                                                  2-nitro-5-aminobenzoic acid                                  2-amino-5-hydroxybenzoic acid                                                                  3-acetylamino-5-aminobenzoic                                                  acid                                                         ______________________________________                                    

Examples of suitable couplers form which the central group B is derivedare:

    ______________________________________                                        1,6-Cleves acid                                                                              8-amino-2-naphthoic acid                                       1,7-Cleves acid                                                                              5-amino-2-naphthoic acid                                       Mixed Cleves acids                                                                           5-amino-2,3-dicarboxynaphthalene                               ______________________________________                                    

Examples of suitable couplers from which the third group C is derivedare:

    ______________________________________                                        Gamma acid     N-butyl-Gamma acid                                             N-methyl-Gamma acid                                                                          N-carboxymethyl-Gamma acid                                     N,N-dimethyl-Gamma acid                                                                      N,N-di(carboxymethyl)-Gamma acid                               N,N-diethyl-Gamma acid                                                                       N-(beta-carboxyethyl)-Gamma acid                               ______________________________________                                    

Examples of suitable compounds of Formula I are given in the followingtable:

    ______________________________________                                        X      W        Y       Z     R        R.sup.1                                ______________________________________                                        3-COOH 5-COOH   H       H     H        H                                      3-COOH 5-COOH   COOH    H     H        H                                      3-COOH 5-COOH   H       COOH  H        H                                      3-COOH 5-COOH   H       SO.sub.3 H                                                                          H        H                                      3-COOH 5-COOH   SO.sub.3 H                                                                            H     H        H                                      3-COOH 5-COOH   COOH    COOH  H        H                                      H      4-COOH   H       COOH  H        H                                      3-COOH 4-COOH   H       H     CH.sub.2 COOH                                                                          CH.sub.3                               2-COOH 5-COOH   H       SO.sub.3 H                                                                          CH.sub.2 COOH                                                                          H                                      3-COOH 5-COOH   SO.sub.3 H                                                                            H     CH.sub.2 COOH                                                                          H                                      3-COOH 5-COOH   H       H     C.sub.2 H.sub.4 COOH                                                                   H                                      3-COOH 5-COOH   H       COOH  CH.sub.2 COOH                                                                          H                                      3-COOH 5-COOH   H       SO.sub.3 H                                                                          CH.sub.2 COOH                                                                          H                                      3-COOH 5-COOH   H       SO.sub.3 H                                                                          C.sub.2 H.sub.4 COOH                                                                   H                                      3-COOH 5-COOH   H       H     CH.sub.2 COOH                                                                          H                                      H      3-COOH   COOH    H     H        H                                      H      3-COOH   H       COOH  H        H                                      H      2-COOH   H       H     H                                               H      4-COOH   H       COOH  CH.sub.2 COOH                                                                          CH.sub.2 COOH                          2-COOH 5-COOH   H       H     CH.sub.3 CH.sub.3                               2-COOH 3-COOH   H       H     C.sub.2 H.sub.5                                                                        C.sub.2 H.sub.5                        2-COOH 4-COOH   H       SO.sub.3 H                                                                          H        H                                      3-COOH 4-COOH   H       H     H        C.sub.4 H.sub.9                        3-CH.sub.3                                                                           5-COOH   H       SO.sub.3 H                                                                          H        H                                      2-CH.sub.3                                                                           5-COOH   H       SO.sub.3 H                                                                          H        H                                      3-Cl   6-COOH   H       SO.sub.3 H                                                                          H        H                                      2-OCH.sub.3                                                                          5-COOH   H       SO.sub.3 H                                                                          H        H                                      3-SO.sub.3 H                                                                         6-COOH   H       SO.sub.3 H                                                                          H        H                                      4-SO.sub.3 H                                                                         6-COOH   H       SO.sub.3 H                                                                          H        H                                      ______________________________________                                    

In the form of salts with a base, especially an alkali metal, ammonia orsubstituted ammonia and mixtures thereof, at pH 7.5 and above,especially from pH 7.5 to 9.0, dyes of Formula I are very soluble inwater, generally to the extend of 10% or more by weight. However, thewater-solubility drops sharply below pH 7.5 and below pH 6 they arevirtually insoluble in water and aqueous media.

The present dye can be converted into its salt with ammonia or an amineby dissolving the dye in the form or a salt with an alkali metal,acidifying with a mineral acid, adjusting the solution to pH 9-9.5 withammonia or the amine and removing alkali metal chloride ions bydialysis.

The present dyes can be made by diazotising a compound which in the freeacid form is of the formula: ##STR3## and coupling with a substitutednaphthalene of the formula: ##STR4##

It has been found that a dye of Formula I can be dissolved in an aqueousmedium above pH 7.5, preferably from pH 7.5 to pH 9, at normalconcentrations which, depending on type of ink required can be up to 20%by weight, but is preferably from 5 to 15% by weight, so that it can beapplied, by any suitable technique, especially ink-jet printing, to apaper substrate. After application of the ink to the substrate andevaporation of the solvent, the dye is at a pH determined by the surfaceof the paper substrate. The natural pH of many paper substrates is suchthat the dye will be be in an environment from pH 5 to 7. Because thewater-solubility of the dye is much lower below pH 7 and virtually zeroat pH 6, it will be more resistant to removal from the substrate bywashing, i.e. it will have a high water-fastness.

We have found also that the water-fastness of the dyes on the paper isincreased if they are printed from an aqueous medium in the form of anammonium or substituted ammonium salt. Examples of amines used to formsuch salts include methylamine, dimethylamine, trimethylamine,ethylamine, n-propylamine, iso-propylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, piperidine, pyridine,morpholine, allylamine, diethylamine, triethylamine and mixturesthereof. It is not essential that the dyes are completely in the form ofthe ammonium salt or substituted ammonium salt and mixed alkali metaland either ammonium salt or substituted ammonium salt are effective,especially those in which at least 50% of the cations are ammonium orsubstituted ammonium ions.

If the natural pH value of the paper surface is significantly above pH6, this can be adjusted downwards, by the addition to the ink of a saltof an acid with a volatile base, such as ammonia. When the ink dries thebase evaporates to leave the free acid which will lower the pH of thepaper surface in the region of the dye. To minimize damage to the paperit is preferred to use a weak acid, such as acetic acid.

A suitable ink comprises a solution of one or two dyes according toFormula I in an aqueous medium.

The ink preferably contains from 0.5% to 20%, more preferably from 0.5%to 15%, and especially from 1% to 10%, by weight of the dye based on thetotal weight of the ink.

Liquid media used for preparing the present ink include water andmixtures of water with various water-soluble organic solvents. Thewater-soluble organic solvents include C₁ -C₄ alkanols such as methanol,ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol,isobutanol; amides such as dimethyl- formamide and dimethylacetamide;ketones or ketone alcohols such as acetone and diacetone alcohol; etherssuch as tetrahydrofuran and dioxane; polyalkylene glycols such aspolyethylene glycol and polypropylene glycol; alkylene glycols andthioglycols containing C₂ -C₆ alkylene groups such as ethylene glycol,propylene glycol, butylene glycol, triethylene glycol; thiodiglycol,hexylene glycol, and diethylene glycol; other polyols such as glycerol,1,2,6-hexanetriol; and lower alkyl ethers of polyhydric alcohols such as2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol,2-[2-(2-methoxyethoxy)ethoxy]ethanol and2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol.

Preferred water-soluble organic solvents among these are glycols andglycol ethers, such as ethylene glycol, diethylene glycol, triethyleneglycol and 2-methoxy-2-ethoxy-2-ethoxyethanol; and polyethylene glycolswith molecular weights up to 500. A preferred specific solvent mixturesis a binary mixture of water and diethylene glycol.

A suitable process for the application of an ink as hereinbefore definedto a paper substrate comprises forming the ink into small droplets byejection from a reservoir through a small orifice by the application ofheat so that the droplets of ink are directed at the paper substrate.

This printing process is conventionally referred to as thermal ink jetprinting and is used to form a record on the paper substrate by theprogrammed application of pulses of heat to the ink adjacent to theorifice during relative movement between the paper substrate and thereservoir.

The invention is further illustrated by the following Examples in whichall parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 Stage 1 1-amino-4-(3,5-dicarboxyphenylazo)-7-sulphonaphthalene

5-Aminoisophthalic acid (18.19, 0.1M) was stirred in water (150 ml) atroom temperature and 2N NaOH added to form a solution at pH 8.0. 2NNaNO₂ solution (50 ml) was added and the mixture stirred to homogenise.The solution was added gradually to a mixture of ice/water (150 ml) and36% HCl (50 ml) at 5° C. and the resulting suspension stirred for 1/2hour at 50° C. Sulphamic acid solution (10%) was added in order toremove excess nitrous acid.

1,7-Cleves acid (22.3g, 0.1M) was dissolved in water (150 ml) and 32%NaOH solution at pH 8.5. Na₂ CO₃ (10g) was added and the solution cooledto 10° C. To this solution was added the above diazo suspension at pH8.0 to pH 9.0 by the addition of Na₂ CO₃ solution (20%). The orangesolution was stirred for 1 hour at 10° C.

10% NaCl (w/v) was added followed by 36% HCl to pH 5.0. The precipitateddye was collected by filtration and washed with NaCl solution (10%, 200ml).

The paste from Stage 1 (0.1M) was dissolved in water (100 ml) and 2NNaOH solution at pH 9.0. 2N NaNO₂ solution (50 ml) was added and themixture stirred 3 minutes. The solution was added gradually to a mixtureof ice/water (150 ml) and 36% HCl (50 ml) at 5° C. using rapidagitation. The resulting suspension was stirred 1h at 5° C. Sulphamicacid solution (10%) was added in order to remove excess nitrous acid.

Gamma acid (23.9g, 0.1M) was dissolved in water (150 ml) and 2N NaOHsolution at pH 9.0. Na₂ CO₃ (10g) was added and the solution cooled to10° C. To this was added the above diazo suspension, while holding thepH at 8.0 to pH 9.0 with 20% Na₂ CO₃ solution. The solution was stirredfor 1 hour at 10° C. and the pH adjusted to 5.5 by the addition ofglacial acetic acid.

The precipitated dye was collected by filtration and washed with diluteacetic acid solution (5%). The paste was redissolved in water (150 ml)and 2N NaOH solution at pH 9.0. The solution was heated to 50° C. andNaCl (15% w/v) added and the precipitated dye collected by filtrationand washed with 10% NaCl solution (100 ml). The product was thetetrasodium salt of1-hydroxy-2-(4-[3,5-dicarboxy-phenylazo]-7-sulpho-naphth-1-ylazo)-3-sulpho-7-aminonaphthalene.

EXAMPLE 2 Stage 1 1-Amino-4-(3,5-dicarboxyphenylazo)naphthalene

5-Aminoisophthalic (18.1g, 0.1M) was diazotised by the method of Example1.

1-Naphthylamine (14.39, 0.1M) was dissolved in water (300 ml) and 36%HCl (15 ml) at 70° C. and cooled to room temperature. The resultingsuspension was added to the above diazo suspension at 10° C. and the pHadjusted to 4.5 by the addition of sodium acetate. The mixture wasstirred for 18 hours and the dye collected by filtration and washed withwater (100 ml).

Stage 2

The paste from Stage 1 (0.1m) was then reacted with Gamma acid by themethod of Example 1, Stage 2. The product was the trisodium salt of1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-naphth-1-ylazo)-3-sulpho-7-aminonaphthalene.

    ______________________________________                                               Dye No.      Liquid medium and other                                   Ink    (parts)      components (parts)                                        ______________________________________                                        1      1 (2.5)      Water (60)                                                                    Ethylene glycol (40)                                      2      2 (2.5)      as Ink 1                                                  3      1 (4.0)      Water (85)                                                                    Diethylene glycol (15)                                    4      2 (4.0)      as Ink 3                                                  5      1 (5.0)      Water (90)                                                                    Diethylene glycol (10)                                    6      2 (5.0)      as Ink 5                                                  7      1 (5.0)      Water (65)                                                                    Glycerol (25)                                                                 Triethanolamine (10)                                      8      2 (3.0)      as Ink 7                                                  9      1 (3.5)      Water (80)                                                                    Ethylene glycol (15)                                                          Polyethylene glycol (MW 200)(5)                           10     2 (3.5)      as Ink 9                                                  ______________________________________                                    

When each of these inks was printed onto plain paper using a piezo orthermal ink-jet printing machine, the printed image obtained had highresistance to water.

EXAMPLE 3

The dye obtained as in Example 1 was stirred in water (400 ml) at pH 8-9until a complete solution was obtained. The solution was then slowlyadded to a mixture of concentrated hydrochloric acid (45 ml) and water(50 ml) and the suspension stirred for 30 minutes and then filtered.

The paste was stirred in water (300ml) and conc.ammonium hydroxide addedto raise the pH to 9-9.5. The solution was then dialysed to removechloride ions and then evaporated to give the mixed ammonium sodium saltof1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-7-sulphonaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.

Inks were prepared as in Example 2 and when printed onto plain paperusing a thermal ink jet printing machine, the printed image obtained hadvery high resistance to water. When the paper carrying the printed imagewas immersed in water or sprayed with a jet of water there is virtuallyno colour loss or deterioration of print quality.

EXAMPLE 4

(a) In place of the ammonium hydroxide used in Example 3 there were usedseparately methylamine, dimethylamine and trimethylamine to give therespective mixed amine-sodium salts of1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-7-sulphonaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.

Inks were prepared as in Example 2 and when printed onto plain paperusing a thermal ink jet printing machine, the printed image obtained hada very high resistance to water.

(b) In place of ammonium hydroxide used in Example 3 there may be usedethylamine, n-propylamine, iso-propylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, piperidine, pyridine,morpholine, allylamine, diethylamine, triethylamine.

EXAMPLE 5

The dye prepared as in Example 2 was converted to the mixedammonium-sodium salt by the method of Example 3.

When converted to an ink and printed onto plain paper using a thermalink-jet printing machine the printed image obtained has very highresistance to water.

EXAMPLE 6

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 2there is used 18.1 g of 4-aminophthalic acid. The product1-hydroxy-2-(4-[3,4-dicarboxyphenylazo]naphth-1-ylazo)-3-sulpho-7-aminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine, the printed image has a very high resistanceto water.

EXAMPLE 7

In place of the 22.3 g of 1,7-Cleves acid used in Example 1 there isused 22.3 g of 1,6-Cleves acid. The product1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-6-sulphonaphth-1-ylazo)-3-sulpho-7-aminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine the printed image showed very high resistanceto water.

EXAMPLE 8

In place of the 22.3 g of 1,7-Cleves acid used in Example 1 there isused 18.7 g of an approximately 50/50 mixture of 5-amino-2-naphthoicacid and 8-amino-2-naphthoic acid. The product consisted of a mixture of1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed very highresistance to water.

EXAMPLE 9

In place of the 23.99 of Gamma-acid used in Example 1 there is used 29.7g of N-carboxymethyl-Gamma acid. The product1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-6-sulphonaphth-1-ylazo)-3-sulpho-7-carboxymethylaminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet machine the printed image showed high resistance to water.

EXAMPLE 10

In place of the 23.9 g of Gamma-acid used in Example 1 there is used31.1 g of N-beta-carboxyethyl-Gamma acid. The product1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-6-sulphonaphth-1-ylazo)-3-sulpho-7-beta-carboxyethylaminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet machine, the printed image showed high resistance to water.

EXAMPLE 11

In place of the 23.9 g of Gamma-acid used in Example 2 there is used29.7 g of N-carboxymethyl-Gamma acid. The product1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-naphth-1-ylazo)-3-sulpho-7-carboxymethylaminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet machine the printed image showed high resistance to water.

EXAMPLE 12

In place of the 23.9 g of Gamma-acid used in Example 2 there is used31.1 g of N-beta-carboxyethyl-Gamma acid. The product1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-naphth-1-ylazo)-3-sulpho-7-beta-carboxyethylaminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet machine the printed image showed high resistance to water.

EXAMPLE 13

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 13.7 g of p-aminobenzoic acid. The product consists of amixture of1-hydroxy-2-(4-[4-carboxyphenylazo]6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[4-carboxyphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.

It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet machine the printed image showed high resistance towater.

EXAMPLE 14

In place of the 13.7 g of p-aminobenzoic acid used in Example 13 thereis used 13.7 g of m-aminobenzoic acid. The product consists of a mixtureof1-hydroxy-2-(4-[3-carboxyphenylazo]6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[3-carboxyphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.When converted to the mixed ammonium-sodium salt by the method ofExample 3 and made into an ink and printed onto plain paper using athermal ink jet machine the printed image showed high resistance towater.

EXAMPLE 15

In place of the 13.7 g of p-aminobenzoic acid used in Example 13 thereis used 13.79 of anthranilic acid. The product consists of a mixture of1-hydroxy-2-(4-[2-carboxyphenylazo]6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[2-carboxyphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet machine the printed image showed high resistance towater.

EXAMPLE 16

In place of the 18.19 of 5-aminoisophthalic acid used in Example 2 thereis used 18.lg of aminoterephthalic acid. The product1-hydroxy-2-(4-[2,5-dicarboxyphenylazo]naphth-1-ylazo)-3-sulpho-7-aminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine the printed image had a high resistance towater.

EXAMPLE 17

In place of the 18.lg of 5-aminoisophthalic a©id used in Example 2 thereis used 18.lg of 3-aminophthalic acid. The product1-hydroxy-2-(4-[2,3-dicarboxyphenylazo]naphth-1-ylazo)-3-sulpho-7-aminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine the printed image had a high resistance towater.

EXAMPLE 18

In place of the 22.3 g of 1,7-Cleves acid used in Example 1 there isused 23.1 g of 5-amino-2,3-dicarboxynaphthalen. The product1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-6,7-dicarboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine the printed image showed high resistance towater.

EXAMPLE 19

In place of the 18.lg of 5-aminoisophthalic acid used in Example 1 thereis used 18.lg of 4-aminoisophthalic acid. The product1-hydroxy-2-(4-[2,4-dicarboxyphenylazo]-7-sulphonaphth-1-ylazo)-3-sulpho-7-aminonapthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine

EXAMPLE 20

In place of the 18.19 of 5-aminoisophthalic acid used in Example 2 thereis used 18.lg of 4-aminoisophthalic acid. The product1-hydroxy-2-(4-[2,4-dicarboxyphenylazo]-naphth-1-ylazo)-3-sulpho-7-aminonaphthalenewas converted to the mixed ammonium-sodium salt by the method of Example3. When made into an ink and printed onto plain paper using a thermalink jet printing machine the printed image showed very high resistanceto water.

EXAMPLE 21

The dye obtained as in Example 1 was stirred in water (400 ml) at pH 8-9until a complete solution was obtained. The solution was acidified withconcentrated hydrochloric acid until the pH falls below 3. Theprecipitate was filtered off, added to water (400 ml) and concentratedammonium hydroxide added until the pH was 7.5-8.0. The solution was thenacidified with concentrated hydrochloric acid and the precipitated dyefiltered off. After repeating the ammonia addition and reprecipitationwith acid three times and finally dissolving in water by adding ammoniumhydroxide to pH 8, the solution was dialysed to remove chloride ions andthen evaporated. The product was virtually 100% ammonium salt of1-hydroxy-2-(4-[3,5-dicarboxyphenylazo]-7-sulphonaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.

When converted to an ink and printed onto plain paper using a thermalink-jet printing machine, the printed image obtained has very highresistance to water. When the paper carrying the printed image wasimmersed in water or sprayed with a jet of water there is virtually nocolour loss or deterioration of print quality.

Alternatively, the ammonium salt of the dye of Example 1 can be obtainedby passing a solution of the sodium salt of the dye down a columncontaining the ammonium form of a cation exchange resin.

EXAMPLE 22

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 15.1 g of 2-amino-5-methylbenzoic acid. The productconsisted of a mixture of 1-hydroxy-2-(4-[2-carboxy-4-methylphenyulazo]-6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene and1-hydroxy-2-(4-[2-carboxy-4-methylphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed very highresistance to water.

EXAMPLE 23

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 15.1 g of 3-amino-4-methylbenzoic acid. The productconsisted of a mixture of1-hydroxy-2-(4-[2-methyl-5-carboxyphenylazo-]-6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[2-methyl-5-carboxyphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed very highresistance to water.

EXAMPLE 24

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 17.1 g of 2-amino-4-chlorobenzoic acid. The productconsisted of a mixture of1-hydroxy-2-(4-[2-carboxy-5-chlorophenylazo]-6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[2-carboxy-5-chlorophenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed very highresistance to water.

EXAMPLE 25

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 16.7 g of 2-amino-4-methoxybenzoic acid. The productconsisted of a mixture of1-hydroxy-2-(4-[2-methoxy-5-carboxyphenylazo]-6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[2-methoxy-5-carboxyphenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed very highresistance to water.

EXAMPLE 26

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 21.7 g of 2-amino-4-sulphobenzoic acid. The productconsisted of a mixture of1-hydroxy-2-(4-[2-carboxy-5-sulphophenylazo]-6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[2-carboxy-5-sulphophenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed highresistance to water.

EXAMPLE 27

In place of the 18.1 g of 5-aminoisophthalic acid used in Example 8there is used 21.7 g of 2-amino-5-sulphobenzoic acid. The productconsisted of a mixture of1-hydroxy-2-(4-[2-carboxy-4-sulphophenylazo]-6-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthaleneand1-hydroxy-2-(4-[2-carboxy-4-sulphophenylazo]-7-carboxynaphth-1-ylazo)-3-sulpho-7-aminonaphthalene.It was converted to the mixed ammonium-sodium salt by the method ofExample 3. When made into an ink and printed onto plain paper using athermal ink jet printing machine the printed image showed highresistance to water.

What is claimed is:
 1. A dye which, in the free acid form, has theformula ##STR5## wherein W is COOHX is selected from the groupconsisting of H, COOH, SO₃ H, halo, nitro, cyano,C₁₋₆ -alkyl, C₁₋₆-alkoxy and C₁₋₆ -acylamino Y is H, COOH or SO₃ H; and Z is H, COOH orSO₃ H;provided that there are at least two COOH groups and that thenumber of COOH groups is equal to or greater than the number of SO₃ Hgroups.
 2. A dye according to claim 1 in which X is COOH.
 3. A dyeaccording to claim 1 containing 2, 3 or 4 CO₂ H groups.
 4. A dyeaccording to claim 1 in the form of its salt with at least one of thebasic compounds selected from the alkali earth metals, ammonia,methylamine, dimethylamine, trimethylamine, ethylamine, n-propylamine,iso-propylamine, n-butylamine, iso-butylamine, sec-butylamine,tert-butylamine, piperidine, pyridine, morpholine, alkylamine,diethylamine and triethylamine.
 5. A dye according to claim 4 in theform of its sodium, ammonium, or mixed sodium/ammonium salt.
 6. A dyewhich, in its free acid form, has the formula ##STR6## wherein Y is H orSO₃ HZ is H, COOH or SO₃ H.
 7. The dye according to claim 5 wherein Yand Z are both H.
 8. The dye according to claim 6 wherein Y is H and Zis SO₃ H.
 9. A dye according to claim 6 in the form of its salt with atleast one of the basic compounds selected from the alkali earth metals,ammonia, methylamine, diethylamine, trimethylamine, ethylamine,n-propylamine, iso-propylamine n,-butylamine, iso-butylamine,sec-butylamine, tert-butylamine, piperidine, pyridine, morpholine,alkylamine, diethylamine and triethylamine.
 10. A dye according to claim9 in the form of its sodium, ammonium, or mixed sodium/ammonium salt.11. A composition of dyes comprising the dye according to claim 6 inwhich Y is SO₃ H and Z is H and the dye according to claim 5 in which Yis H and Z is SO₃ H.
 12. A composition of dyes comprising the dyeaccording to claim 6 in which Y is H and Z is COOH and the dye accordingto claim 5 in which Y is COOH and X is H.